Infectious necrotic hepatitis is a disease of large animals, especially

sheep Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus '' Ovis'', in everyday usage it almost always refers to domesticated ...

, caused by ''

Clostridium novyi ''Clostridium novyi'' (oedematiens) a Gram-positive, endospore- forming, obligate anaerobic bacteria of the class Clostridia. It is ubiquitous, being found in the soil and faeces. It is pathogenic, causing a wide variety of diseases in man and an ...

'' infection. The primary infection is intestinal and transferred by the faecal-oral route. Spores of ''C. novyi'' escape from the gut and lodge in the

liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...

, where they remain dormant until some injury creates

anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: * Anaerobic adhesive, a bonding a ...

conditions for them to germinate, causing local necrosis and widespread damage to the microvascular system, resulting in subcutaneous bleeding and blackening of the skin, hence the common name "black disease".

In sheep

, the disease, referred to as "black disease", results from interaction of bacteria (especially ''C. novyi'') and liver fluke (''Fasciola hepatica'').

Symptoms

As with other enterotoxemias, the disease leads to sudden death. Nevertheless, sheep with previous vaccination can show a protracted course. The rest of the flock may show loss of appetite and pica.

Post-mortem lesions

Peritoneal and thoracic cavities contains a great quantity of fluids, as does the pericardial sac. The liver is sometimes swollen with perihepatitis. There appear a great number of necrotic foci, 3 to 4 mm diameter, which extend deeply in the organ. Hepatic lymph nodes are enlarged. The

gallbladder In vertebrates, the gallbladder, also known as the cholecyst, is a small hollow organ where bile is stored and concentrated before it is released into the small intestine. In humans, the pear-shaped gallbladder lies beneath the liver, although ...

is full. Subcutaneous tissues are full of cyanotic venous blood. They may darken the hide, hence the name "black disease".

Control

In order to control for the disease, the ''Lymnaea'' spp snails, which are the intermediate host for the liver flukes, need to be controlled. There are three ways that have proven most effective when controlling the snail populations: * The first is by treating pastures and water channels with copper sulfate. This method is not always practical, because it is too expensive to treat in large areas. Lack of cooperation between neighbors is also a problem, snails are easily transported, and treated pastures become re-infested by neighboring fields and streams. * Drenching the sheep with carbon tetra-chloride in paraffin oil has proven to be an alternative. However, drenching in more than recommended doses can be fatal, by causing liver damage, which could initiate the disease in sheep carrying ''B. oedematiens'' spores. * Drainage is an effective option to eliminate the snails. However, draining the places where the grass grows eliminates a source of food for the sheep and creates other unwanted problems.

References

{{Commons category, Infectious necrotic hepatitis, infectious necrotic hepatitis Sheep and goat diseases Animal bacterial diseases